1. Field of the Invention
The present invention relates to an overhead projector (OHP), and more particularly to an overhead projector of the reflective type for reading subject copies based on reflections therefrom of light applied thereto.
2. Description of the Prior Art
As is well known in the art, conventional overhead projectors apply light to a subject copy, detect the light transmitted through or reflected by the illuminated subject copy, and project an image represented by the detected light onto a screen. The subject copy is read and its image is projected onto the screen, using a single light source. Therefore, the light source should have output power settings that meet requirements for best qualities in both the reading of the subject copy and the projection of the image.
Subject copies whose images are to be projected are available in a wide range of different qualities or conditions. Some subject copies carry images of low contrast, have colored backgrounds, and are reflective of light. Therefore, the light source of an overhead projector may not provide desired illumination for every subject copy, and the overhead project may possibly be used to project images under undesirable illuminating conditions. For example, if the light source of an overhead projector is adjusted for better contrast of an image read from a subject copy, then the brightness of the image projected onto the screen may be lowered.
Most earlier overhead projectors are designed only to display subject copy images, but not to print, electronically store, and process the information contained in the projected images. However, recent opportunities for presentations using overhead projectors often pose demands for overhead projectors which can print projected images immediately at sites where they are projected, or which can process projected images with the aid of a computer.